Stereoscopy, stereoscopic imaging, or three-dimensional (3-D) imaging is any technique capable of recording 3-D visual information or creating the illusion of depth in an image. The illusion of depth in a photograph, movie, video game, or other two-dimensional image is created by presenting a slightly different image to each eye. Many 3-D displays use this method to convey images. Traditional stereoscopic imagery includes creating a 3-D illusion, starting from a pair of 2-D images. The easiest way to create depth perception in the brain is to provide the eyes of the viewer two different images, representing two perspectives of the same object, with a minor deviation similar to the perspectives that both eyes naturally receive in binocular vision.
Various types of 3-D imaging techniques are known, including polarization encoding of the light bound for each eye with different polarizations. Such schemes may involve using orthogonally linearly polarized states, or circularly polarized states of opposite handedness.
With respect to linearly polarized 3-D schemes, to present a stereoscopic picture, two images are projected superimposed onto the same screen though orthogonal polarizing filters. It is best to use a silver screen so that polarization is preserved. The viewer wears eyeglasses, which also contain a pair of orthogonal polarizing filters. As each filter only passes light, which is similarly polarized and blocks the orthogonally polarized light, each eye only sees one of the images, and the effect is achieved. Linearly polarized glasses require the viewer to keep his or her head level, as tilting of the viewing filters will cause the images of the left and right channels to bleed over to the opposite channel (also known as crosstalk). In addition, since no head tracking is involved, several people can view the stereoscopic images at the same time.
With regard to the circularly polarized 3-D image systems, to present a stereoscopic picture, two images are projected superimposed onto the same screen through circular polarizing filters of opposite handedness. The viewer wears eyeglasses, which contain a pair of analyzing filters (circular polarizers mounted in reverse) of opposite handedness. Light that is of left-circular polarization is extinguished by the right-handed analyzer; while right right-circularly polarized light is extinguished by the left-handed analyzer. The result is similar to that of stereoscopic viewing using linearly polarized glasses, except the viewer can tilt his or her head and still maintain left/right separation. Lipton, in U.S. Pat. No. 4,792,850, uses electronically driven circular polarizers that alternate between left and right handedness, and do so in synchronization with the left or right image being displayed by the movie projector. Direct view displays may also be used to encode the polarization states for different eyes, for example, by having alternate pixels of polarization encoded. Another possibility is when a single display or projector creates alternate right/left eye images that are actively encoded using a polarization switch, such as that disclosed in commonly-assigned patent application Ser. No. 11/424,087, entitled “Achromatic Polarization Switches” filed Jun. 14, 2006, which is hereby incorporated by reference.
Polarized motion pictures have been around since the middle of the twentieth century. In order to watch such a movie, the viewer is usually given a pair of paper or plastic polarization glasses to wear to watch the show. However, such glasses can be expensive to produce, and offer a relatively low performance, which can cause the viewer to incur eye strain, headaches, and generally a negative perception of stereoscopic imagery. Accordingly, it would be desirable to have a method and apparatus for producing high performance and low-cost stereoscopic eyewear.